1. Field of Invention
The present disclosure relates in general to pressure assisted blowout preventer, and more specifically relates to using wellbore pressure to assist actuation of an operator in a blowout preventer.
2. Description of Prior Art
Wellbores in hydrocarbon bearing subterranean formations are formed by rotating a drill bit mounted on a lower end of a drill string. Typically, a wellhead housing is installed at the earth's surface and through which bit and string are inserted. A blow out preventer (BOP) stack usually mounts on top of the wellhead housing that provides pressure control of the wellbore, and often includes rams to shut in the wellbore should pressure in the wellbore become uncontrollable. Additional rams are often included with BOP stacks that are for shearing the string within the BOP stack, and also for pressure testing within the BOP. Further typically included with BOP stacks are flow lines and valves to allow fluid flow through the BOP stack for remediating overpressure in the wellbore.
Wellbore pressure communicates to inside the wellhead, and thus to the BOP; which generates a force that opposes ram and packer actuation. Pressure increases in the wellbore further increasing the force opposing ram and packer movement, thereby increasing the amount of force required for actuating the ram and packer. Rams and packers are generally hydraulically powered, and often by systems having limited capacity. Because a typical BOP is regularly tested, the resistive force created by wellbore pressure results in more frequent replenishment of the system, or installing actuation systems having larger capacity. Hydraulic systems with large capacity are not only costly, but impractical in some subsea applications.